Mirabelle de Nancy plum trees are partially self-fertile, but you’ll enjoy a larger harvest and better quality fruit if a pollinator is located nearby. Remove water sprouts as they pop up throughout the season. If your soil is nutrient-rich, no fertilizer is needed until the tree begins bearing fruit, usually about two to four years. You can prune the tree while it is dormant in winter or in summer. When you prune in the winter, you revitalize the tree and stimulate growth the following spring, whereas when you do it in the summer, you slow unruly growth and limit the size of the tree. Nederlands: Pruimenzaden planten. How to prune plums. Runner Beans, Swiss Chard, Delicious summer treats, Plums bear abundant crops in our region and throughout the U.S. Prune on a dry day and use and they are: